The approaches described in this section are approaches that could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.
Segmentation of a digital image involves identifying regions in the image based on some predefined criteria. These criteria may be contextual, numerical, shape, size, and/or color-related, gradient-related and more. A background/foreground segmented image can be used in numerous digital image processing algorithms such as algorithms to enhance the separation of a subject in the foreground from the background in order to enhance depth of field, to enhance or eliminate the background altogether, or to extract objects such as faces or people from an image. A background/foreground segmented image can also be used for numerous image processing operations that include image enhancement, color correction, and/or object-based image analysis.
A digital image acquisition system with no film can include an apparatus for capturing digital images, a flash unit for providing illumination during image capture, and a segmentation tool. The segmentation tool can distinguish an object, such as a person, in the foreground of a captured digital image from a background of the captured digital image. One technique for performing the segmentation comprises comparing an image taken with a flash to an image taken without a flash. For example, the non-flash image might be taken immediately before the flash image, and the non-flash image might be taken at a lower resolution in order to improve device performance. The foreground of the image can be determined by identifying a change in intensity between portions of the flash image and corresponding portions of the non-flash image. Due to proximity to the flash, an object in the foreground of an image will experience a higher change in intensity when captured with a flash than will objects in the background.
The technique of measuring a change in intensity between portions of a flash image and portions of a non-flash image, however, has some limitations. For example, in a digital image, it is common for a person's head to not be properly illuminated by a flash because of the angle the light reflects off of the top of the head. Instead, it is common for a person's head to be strongly illuminated by ambient illumination, such as the sun, resulting in a difference in intensity in that particular area (top of the head) that is lower than other areas of the person, and thus indicative of being part of the image's background even though it is part of a foreground object.